The purpose of this study is to better understand the effects of chronic stress on mothers and their infants. Women are prone to chronic stress and stress-related disorders (e.g., depression, anxiety) within the first year of giving birth, and thee maternal experiences are known to have an adverse effect on infants' development including the organization of their HPA axis and other stress related systems. Unfortunately,, not only are there few studies pertaining to the effects of chronic stress on mothers and infants, but the measurement of chronic stress in any population is problematic. Assessing chronic stress is particularly difficult in populations such as infants, since subjective report from others falls shrt of identifying the infants' experience. Biological measures of chronic stress often rely on measures of basal levels of cortisol. However, it is quite possible that assessments of cortisol from saliva, blood, and urine and the requirement with these measures to capture multiple time points do not adequately capture the chronic levels of stress that they purport to measure. The goal of this project is to evaluate the use of hair cortisol as a biomarker for chronic stress in mother-infant dyads. Hair cortisol is an emerging biomarker that may be an effective method for measuring HPA activity, as it can provide a longer retrospective calendar (e.g., 3- to 6-months) of chronic stress compared with measures of cortisol from other sources. From a practical standpoint, the sampling and storage of hair cortisol may be less cumbersome than the current procedures required from cortisol collected from saliva, blood, or urine. Hair cortisol may provide an effective marker for such stress related disorders and be an important tool for determining risk of later developmental problems among infants. To accomplish our goal, we will use a longitudinal design that follows two cohorts high risk (n=80) and low risk (n=80) mother-infant dyads at 9 months (T1) and 12 months (T2) postpartum. By using up-to-date hair cortisol sampling and assay procedures, we expect that the hair sampled from mothers and infants at these time points will provide retrospective cortisol data from the previous 3 months (T1: 6-9 months, T2: 9-12 months). Reported chronic stress, depression and anxiety symptoms, and trauma exposure will also be collected from the mother through questionnaires and interviews. We plan to calculate differences in hair cortisol across groups, associations between mother and infant hair cortisol, and associations of hair cortisol levels with reported chronic stress. We expect the high risk group to have higher levels of cortisol than the low risk group, positive associations of the hair cortisol levels of mothers and infants, and positive associations of the hair cortisol and reported chronic stress. Because hair cortisol is a new measure and has never been used with mother-infant dyads, we will track participant recruitment rates. This project has the potential to establish a useful and efficient biomarker for chronic stress while propelling our understanding of the mechanisms (factors and moderators) that underlie chronic stress and adverse outcomes in mothers and infants.